1. （坚果的）仁，核
The kernel of a nut is the part that is inside the shell.

2. 核心；中心；要点
The kernel of something is the central and most important part of it.

3. 一小部分
A kernel of something is a small element of it.

1. the choicest or most essential or most vital part of some idea or experience

e.g. the gist of the prosecutor's argument
the heart and soul of the Republican Party
the nub of the story

Synonym: substancecorecentercentreessencegistheartheart and soulinwardnessmarrowmeatnubpithsumnitty-gritty

2. a single whole grain of a cereal

e.g. a kernel of corn

3. the inner and usually edible part of a seed or grain or nut or fruit stone

e.g. black walnut kernels are difficult to get out of the shell

Synonym: meat